text:
Tailplane/Equilibrium conditions
In regards to achieving equilibrium conditions, what is the relation between airspeed and the tailplane?

Did you perform basic research? if so, what didn't you understand? Your question must be quite more precise. see the help center for more information.

This is the third time this week I provide a link to the same section of how it flies. Thus I think you can find in aviation.SE parts of the information you seek and come back with a more precise question about aspect not yet discussed on this website.

The article you link is a teeny tiny bit off.  The tail of a non-canard NEVER produces vertical lift in any steady state condition.  Only in transient conditions, mainly those where an elevator input drives a ND pitch rate that exceeds exceeds the inherent nose down pitching moment. An airplane with a CofG that required a tail to lift up would be uncontrollable for any length of time.  In steady state flight there is always downforce.

I think it may be a bit unclear what exactly you're asking.  What do you mean by the tailplane?  Do you mean the relationship between the horizontal stabilizer, center of gravity, and lift?

@JohnK I think you will agree that a tandem wing can be stable and that the rear wing provides lift. If the rear wing is progressively shrunk to the size of a tail plane, at what point do you imagine it must reach the crossover point between lift and downforce, and why?

@JohnK Please stop spreading this nonsense. Of course is it entirely possible for a tail to produce lift in a steady state condition. Slow flight, no flaps and a rear center of gravity are all what is needed.

@PeterKämpf yes in theory you can have an airplane fly with the CG aft of the neutral point creating a net pitch up moment so the tail is forced to lift up to keep the nose from rising, but it will be very unpleasant, with forward elevator pressure or ND trim required to keep from slowing more, and you wouldn't get me flying it.  Not aware of any normal airplanes designed to do that.

To be statically stable in pitch, the tail has to generate a downforce that opposes a continuous nose down pitching moment.  Everything else being the same, more speed increases downforce, less speed decreases it.  The equilibrium state is when the opposing forces are in balance in steady state flight, hands off the controls, and the airplane is said to be "in trim".  This is achieved at a given airspeed for a given set of "configuration of forces" you might say (pitching moments, thrust lines, C of G positions etc) and is called "trim speed".
Trim speed is the speed at which tail downforce balances the nose down pitching moments to achieve equilibrium (not accelerating or decelerating) for a given set of physical conditions.  FAR 25 static stability requirements require the plane to positively seek this speed by pitching uphill or downhill when disturbed from that speed in an attempt to regain equilibrium.
So the relation to the tailplane is that speed in excess of trim speed causes the nose to pitch up due to excessive downforce, which makes it go uphill and slow down, trying to get back to that equilibrium state.  Vice versa when speed is less than trim speed; it pitches down trying to get to the equilibrium state.  In an actual airplane it overshoots its equilibrium point several times trying to get there and eventually zeros in (the Phugoid oscillation).
Some other configuration change, a power change, a C of G change, a dragging item change, a flap sticking down, or elevator incidence change, will alter the speed at which equilibrium is achieved or trim speed. Once stabilized at a new trim speed, it will now seek the revised trim speed as before, if disturbed, as the tail responds to downforce changes with airspeed as described.

For a different view see https://aviation.stackexchange.com/a/77188/34686 , https://aviation.stackexchange.com/a/30720/34686 , https://aviation.stackexchange.com/a/76837/34686 (including embedded links to See How It Flies website sections) , https://www.rcgroups.com/forums/showpost.php?p=26413333&postcount=2 -- note sentence "Some free flight airplanes actually balance behind the trailing edge of the wing."

You can balance anywhere you want as long as the net result is a ND pitching moment for the tail to oppose.  A horizontal tail lifting up in steady state conditions would require ND trim to slow down and would be rather dangerous and unpleasant to fly.

Another good one-- https://aviation.stackexchange.com/a/22090/34686

@quiet flyer Sorry, but the flying wing gets its pitch stability from downforce opposing a pitching moment also.  It's just that the downforce is coming from the local area of the trailing edge where the elevator is. It's just the horizontal tail moved forward to the wing trailing edge.  The arm it has to work on is very short, so the pitching moment has to be very low using airfoils designed for the purpose.  For this reason, flying wings suffer from two problems - overly light and sensitive pitch control, and a very limited CG range.

@JohnK Downforce is quite unnecessary - we have known how to make a lifting tail stable since around 1918. What you are thinking of is the relative change in moments around the centre of lift, which is a function of the lift slope coefficients of the two surfaces. For stability, the tail must exert a lift moment change greater than change in wing lift moment. The absolute direction of the force is unimportant.

@GuyInchbald you're describing a canard or tandem wing where the lift slope of the forward wing has to be steeper than the aft one for it to work at all.  The Rutan canards and tandems all use that.  Rutan used the UofGlasgow airfoil on the ezes and the quickies because its unique lift slope characteristics gave strong static stability.  Conventional tailed airplanes don't even need an airfoil. Anything to deflect the air will do.  Like the flat plate elevator-stab you see on any fabric covered light plane.  If a jet had an up lifting tail, the tail's LE would have to move up to slow down.

@JohnK You really do need to think harder about the borderline between a small rear tandem wing and a large tail plane. You have been downvoted at least twice for a reason.

Hey compared to PSE this is heaven when it comes to downvotes lol!

@GuyInchbald the post is about how regular aircraft respond to speed changes.  I explained how normal airplanes trim to a speed.  Tandem wings planes are not relevant to the question.  Perhaps your comment is related to the other post about tandems.

@JohnK I was commenting on your wholly misguided comment, not on the original question. meanwhile, I see that someone has indeed marked this question as a duplicate of one about tandems.


text:
Is there an ideal value for the difference between the stick fixed and stick free static margin?
I'm calculating the static stability for a fictional  aircraft and have to determine the elevator size. I have all the calculations but don't know how to choose the correct size and position. Is it ideal to have the difference between the sitck fixed and stick free static margins as close to 1 as possible or should the differnece in the margins be large?
Thankyou in advance, covid-19 has meant that we're not able to access univeristy resources to gain our knowledge as usual.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why is one exhaust directed upwards?
This is the first Cessna Skycourier during certification. Why are the two exhausts oriented upwards?

Does this answer your question? why some airplanes have their exhaust gases vectored above the wing?

The rotation direction of the propellers produces a rotating slipstream.  This slipstream pushes the exaust from the (engine's) right side downward, but the exhaust on the other side would be pushed up, producing potential heat problems where it impinges on the wing (as well as depositing lots of soot).  By bending the exhaust pipe upward as you see, the exhaust on that side passes over the wing, in an airstream that will both protect the wing surface from the exhaust heat and reduce soot deposition.

So both comments and the answer answered my question, to whom do I give credit? I'd like to give each person due credit.

@Raffles This is why these sites discourage answers in comments (links to duplicates are a special case): we can't vote them up or down or give the author credit/rep.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
In cases where it's legal, is it feasible to use a phone for a call in the normal way?
In a country that allows cell phone use on planes, or with VoIP using satellite Internet, how feasible is it to use a phone by the normal method of holding it to your face on a small GA plane such as a Cessna 172? Is it too loud?

Blue tooth headsets work well for this.

My way of using a cell phone for many years has been a bluetooth headset, similar to this one from Amazon. They don't cost much. A must for driving, but basically anywhere - around the house, office, walking, etc. In other words, I don't consider "holding it to your face" to be "normal method".

I've made a call 3 times from a light GA aircraft. 2 of those were on the ground with the engine running - once using a noise cancelling bluetooth headset and the other holding the phone to my ear. The time the phone was held to my ear it was very hard to hear the other end and they were very aware that I was in a very noisy environment. The time using my headset the callee was completely unaware that I was in the aircraft and I could hear them clerarly.
That probably says a lot about a decent directional microphone and decent noise cancelling - but I'd say that anecdotally with very little data the answer to your question is that it is indeed too loud to realistically use a phone in the normal way in a light GA aircraft such as a C172.


text:
Why are there not more emergency squawk codes?
7500 is used for hijacking, 7600 for radio failure, and 7700 for any other emergency. I understand that 7600 and 7500 need special handling (you can't talk to ATC if your radio has failed, and a hijacked plane may need a military escort), but why not for other emergencies? For example, why isn't there a "fire" code so the airport can have firefighting equipment ready?

7400 is used by a UAS which has lost its connection to its remote pilot.

The airport should have firefighting equipment ready in the event of any emergency. Whether there is already fire on board, a crash will start a fire about 90% of the time.
Every emergency is unique and different. Their handling by ATC is mostly the same: give the plane absolute priority, ground or divert whoever you have to, have equipment ready, be prepared to call for rescue. Not much more that can be done.


text:
Are there procedures for pilots to handle loss of ATC at normally-towered airports?
Are there procedures for pilots to safely handle a situation in which ATC loses the ability to communicate (complete loss of power, incapacitation of all controllers, etc.) at a busy towered airport?

That's a fairly broad question - VFR, or IFR?  Tower controllers, or radar?

@MichaelHall I was primarily thinking of airliners, so IFR. I don't quite understand your second question?

Well, radar controls sequencing of IFR traffic at large Class B and C airports so that would be a pretty big deal.  However, a busy GA airport on a VFR day with pilots working the landing pattern would probably adapt much better since most pilots are trained on communication at non-towered airfields.   There would probably be a few go arounds and some radio chatter before people started calling out their own position and looking for light signals from the tower.  I've been in the pattern when the tower controllers say goodnight and leave for the day.  It just reverts to E.

I don't want to mod-hammer this, but it's a pretty close dupe of https://aviation.stackexchange.com/q/13438/7532

@MichaelHall if someone was interested in all 4 of those scenarios, should they ask 4 different questions? Is it not possible for an answer to succinctly answer them all? For example to my knowledge there will be very little difference in procedure for IFR and VFR flights when the tower closes, compared with their normal operations in uncontrolled airspace.

@Ben, not necessarily...  I just mentioned it in case it helped the OP focus.  If someone is only interested in large jetliners it might save some typing from a person answering.  I've invested time and energy in drafting what I though was a good answer before only to find out the person was really focused on something else.

Yes. Regardless of the source of the communication loss, much of the procedural framework in IFR, detailed clearances and flight plans, standard profiles for this and for that, Standard Instrument Departure procedures, Standard Terminal Arrival procedures, are to make it safe to complete a trip after a communication loss.
While in communication with ATC, you just do what you're told by the controller, and technically, none of those published procedures and protocols are really necessary when you just have to follow instructions.
When a comm failure happens, you notify ATC by selecting the Comms Failure Code 7600 on the transponder. The standardized procedures, and your clearance, gives you a path to take, and which ATC can assume you'll take to complete your trip.
When there isn't a specific published routing to follow, you are expected to find your way there by the most logical path so the controller can anticipate what you're going to do. For example, if you're on radar vectors to an approach and there is a comm failure, and you select 7600, the controller can anticipate that you'll navigate to the final approach path by the most obvious route and carry on with the approach and landing, and will make sure other airplanes stay out of your way.
If the comm failure was at the other end, at a control tower, the pilot would try another frequency before assuming there was a comm failure in the plane. For example, if handed off to tower by the arrival controller, usually when established on final, and tower didn't respond when checking in, the pilot would switch back to the arrival controller's frequency and let them know what's going on or check that they got the tower frequency correct.
However, in that case, it's likely that the arrival controller, who is at another location offsite, already knows about whatever crisis has befallen the tower, and ATC will be sending airplanes elsewhere anyway.


text:
What exactly did Trent Palmer do that was supposedly "wrong"?
https://www.aopa.org/news-and-media/all-news/2023/april/19/trent-palmer-battles-faa-over-word-necessary
To summarize, he made a low pass over a potential off-airport landing site to check whether or not it was suitable. He says that it was legal because it was necessary for the purpose of landing; the FAA disagrees. They are also charging him with careless or reckless operation.
What exactly did he supposedly do wrong? Wouldn't it be reckless to land on an unfamiliar site without making a low pass to assess the suitability of the landing site?

I think he would've been far better off asserting that he had the intention to land, and did a normal "go-around" after seeing unacceptable conditions on the landing surface.  He would be allowed to go very low if he planned to land.  Going below 500 ft purely for a visual inspection is what is in doubt and being litigated.

I'm not arguing in favor of the FAA's decision, but there was some subjective evaluation of the video, he got as low as 30 feet, and he is a popular "YouTuber" with some incentive to show off just a little to attract viewers.  I haven't seen the video of this specific incident, but would wager it was a little "extra" from what is normally needed to assess an off airport landing site.  Especially since his friend could have cleared rocks and prepped it for him...

@abelenky It's unlikely to have worked as a defense, since part of the judge's decision is that the strip was "unsuitable for landing" outside of an emergency, and that Palmer should have been able to determine that from "Any reasonable ground assessment, or a navigation map, or even a Google Earth view."

@Chris so it would have been legal if it weren't obvious that it was unsuitable?

@Someone Possibly. Palmer would have also needed to convince the judge that it was necessary to pass so close to the people and structures that he did. Given that he admitted that there were other routes he could have taken, that would be difficult to impossible. It wouldn't necessarily protect him from the 91.13 issue, either.

Remember it's not "500 feet, unless you are landing." It's "500 feet, unless necessary for landing." Admitting that there were alternatives that would work seems pretty damning to his defense.

And if it were necessary, the very fact that it's necessary to get that close to a residence in order to land safely arguably makes it an unsuitable landing spot.

Specifically, the FAA alleges that Palmer:

operated at altitudes of less than 100 feet above ground level and, more specifically, operated within
approximately 50 feet of a stable, shed, or propane tank; within approximately 100 to 150 feet of a residential home at 400 Desert Sun Lane; within 100 to 150 feet of an adult and child outside of the home; and within 300 feet of 2 adults and 2 children outside of the home and near the perimeter of the property.

The above is quoted from the NTSB order reaffirming the 120-day suspension.
The administrative law judge presiding over the case changed all of the distances to "within 500 feet," since there is inadequate evidence of the exact distances involved, but the evidence suggests that it was less than the 500 feet mentioned in 91.119(c).
The FAA maintains that low passes are not allowed to violate the altitude restrictions of 91.119. It further maintains that Palmer's intended landing spot was unsuitable for landing, and uses his own testimony and decision not to land as evidence. Also that Palmer was undertaking dangerous maneuvers at high bank angles that were unnecessary for landing.
Palmer admitted that there were alternative flight paths that could have kept him farther away from structures and still given him an appropriate viewing of the landing spot, and that he did not consider these alternatives.
The judge agreed that the spot Palmer chose was "unsuitable for landing" outside of an emergency, and that Palmer should have been able to determine that from seeing the nearby residences and structures from "any reasonable ground assessment, or a navigation map, or even a Google Earth view." Since the landing spot is unsuitable, nothing Palmer was doing could have been "necessary for landing," and so he is not excused from the requirements of 91.119.

I would have argued that even if the land was not presently immediately suitable for landing, the inspection was an essential part of the operational sequence "record footage of intended landing strip; temporarily land elsewhere; inspect footage while safely on ground; make necessary changes to strip; take off; land on strip", any safe landing on the strip would require first doing a visual inspection from the air, and recording camera footage and inspecting it later would be safer than trying to inspect the strip while flying the plane.  Even if the strip was known not to be in condition...

@supercat Given that the landing spot is intended for UAS, and UAS can hold cameras, that wouldn't be particularly convincing to me.

...for immediate landing, a multi-camera aereal inspection could have aided the process of deciding whether some strip placements would make landings more or less safe than others.

I would also argue that (if my understanding of the facts is correct) the condition of the field was reasonably believed to be such that an engine failure would result in an uncomfortable but not life-threatening landing.  Also, I've not flown an aircraft, but I would think that if one is trying to land at an airstrip without PAPI lights, it's useful to have certain reliable visual landmarks to indicate whether one is on a good glide slope.  I don't know how well one could estimate without being an aircraft what kinds of visual references would be most suitable, and where...

...a landing strip should best be placed to make use of them.

In the FAA's opinion (and judgement!), his flight was contrary to CFR 91.119 specifically, flying within 500ft of a person, vehicle, ship or structure over a populated area.
In addition they say he operated outside of CFR 91.13 which covers reckless operation of an aircraft.
The judgement states:

The law judge ruled that the Administrator proved by a
preponderance of the evidence that respondent operated a low altitude flight in violation of 14
C.F.R. §§ 91.119(a), (c) and 91.13(a) but identified mitigating factors justifying a reduced penalty

So the ruling was that making sure it's safe to land is not a necessary part of landing? It seems like not doing so would be illegal.

@Someone The ruling was that making sure it's safe for landing could be done correctly and safely above 500ft. Therefore the unstated meaning of the ruling is that Trent's excuse was just an excuse (a.k.a. BS)

Palmer called it an "inspection pass" and not a "go-around".
A "go-around" is a very different thing in the eyes of aviators.  There are two huge and opposing forces on go-arounds: foolish pilots trying to stick bad approaches plus tremendous pressure from "the company" to avoid the fuel cost and dispatching impact of a go-around. Versus, everyone who cares about safety, pushing back to protect pilots so they are free to choose go-arounds when warranted, without any fear of consequence or blowback.
Palmer should have argued that of relying on the  friend's claims that the field was fit for service, and was intending to land.  Then claimed to unexpectedly see something that made the field unfit, so went around and then diverted to an alternate field. At that point people would be getting on their feet to defend the call.
As things are, Palmer flat admitted this was not quite really an airport, hence warranting an off-airport-style inspection pass, and that could've been done from 500 feet.  I don't know the particulars but I'd bet that the obstruction that caused Palmer to cancel the landing was readily visible from 500 feet.
So, this is a mess.  Right now, it's doing the worst thing imaginable, which is to encourage pilots to head straight in and try to stick landings on marginal or defective sites that look worse and worse the closer they get.  Because if they go around, well, then, that's an "inspection pass" and they're in the soup right next to Trent.
I think the fallout here is going to be, well, hopefully some refinement of the procedure for off airport landings.
The FAA had literature which advised pilots do arguably what Palmer did, so there's probably going to be an acquittal on appeal.   The punishment here is not severe, so the case is entirely about "the principle of the thing" e.g.  defining statutory, clear "lines in the sand" to guide future sport pilots.  I completely support Trent's willingness to appeal, because I think "good law" (well, good regulation) will come out of it.


text:
Is it normal to fly or glide only one mile per hour above stall speed?
At one point, Through Gates of Splendor describes Nate Saint gliding in his Piper PA-14 Family Cruiser at 45 mph; the plane's stall speed is 44 mph. Earlier in the book, he flew at 45 mph. Is it normal and safe to fly or glide only one mile per hour above stall speed in a small airplane? When gliding, he started at 3,000 feet and "throttled all the way back [and] pulled flaps"; could "pull[ing] flaps" have lowered the stall speed? I don't remember something like this being described when he flew under power at this speed, nor do I remember the book mentioning his altitude.

Stall speeds are specific to a configuration, such as flaps up or flaps down (or also various intermediate flap settings), as well as power-on and power-off (more so in some aircraft than others). Stall speed also varies with aircraft weight, so to say that this aircraft stalls at XX mph is a simplification -- often speeds are published at a maximum weight, so in lighter cases you'll stall slightly slower.  Also, speeds may be published (and described) in MPH or in Knots.  Until you know exactly what case the "44 mph" value describes, saying that 45 mph is 1 mph above stalling may be dubious.

@RalphJ the 44 mph stall speed is with flaps down. Would "pull[ing] flaps" put them up or down?

Indicated airspeed is not a true representation of the actual stall speed. If you practice stall in an actual aircraft, often it will stall at an indicated speed well below the published stall speed.

could "pull[ing] flaps" have lowered the stall speed?

Yes, it absolutely would.  ("Pulling" means "lowering", especially in the context of the PA-14 where the flaps were controlled by a simple mechanical lever that you actually "pulled" on to lower the flaps.)
You'll find evidence in support of this reduction in stall speed if you peruse any airplane flight manual (so long as said airplane has flaps.)
A reduction in the neighborhood of 5-7 mph would seem typical for light airplanes.
Keep in mind also that distance from ground, and smoothness of air, are two factors that hugely affect the safety (or lack thereof) of flying very near the stall speed.  Also the stall characteristics of the aircraft.  If you are just going to feel a gentle burble over the tail, which know you can stop by just easing the stick/yoke forward a tad, and if you fail to do that the nose will just gently start to drop a bit with the wings staying level, and you are high above the ground, and there's no turbulence, then there's very little danger in flying right up to the "edge" of the stall.
Btw, stall speed also varies according to the square root of the gross weight.  Published stall speeds are for a specific gross weight-- likely the maximum gross weight allowed.  Unless the author specifically stated that the aircraft was flying "1 mph above the stall speed", one should be careful about jumping to conclusions based on a published stall speed corresponding to one specific gross weight.
Throttling "all the way back", on the other hand, will typically very slightly increase the stall speed in a single-engine prop plane of conventional configuration.  But the published stall speed is likely for the power-off configuration anyway.

Thank you! The 45 MPH stall speed is with flaps down, but the other factors affecting the stall speed could definitely have made it more than a 1 MPH difference.

As usual, lift $L$ generated by a wing can be expressed by:
$L=½\rho V²SC_l=W$
where $W$ is the airplane's weight, $\rho$ air's density, $V$ speed of flight, $S$ wing surface and $C_l$ lift coefficient. $C_l$ has a typical trend like shown in the following picture (source - $A$ is the aspect ratio):

As visible, $C_l$ increases proportionally to the angle of attack $\alpha$ until the wing can't get anymore and it just stalls: we reached the maximum lift coefficient $C_{l_{max}}$ that can be extracted from the wing before it stalls.
If we now rewrite the previous lift equation in respect to $V$, we see how the stall speed changes:
$V= \sqrt{\frac{W}{½\rho S C_l}} \Rightarrow V_{stall}= \sqrt{\frac{W}{½\rho S C_{l_{max}}}}$
From the latter equation it can be seen that the stall speed depends not only on the wing configuration (via $C_{l_{max}}$) but on density and weight as well. In particular, a heavier airplane implies higher stall speed i.e. the need to fly faster to stay away from stall; and also flying higher (lower $\rho$) has the same effect.
So stall speed is not one single value but it depends on the flight conditions.

In gliders, yes.
When thermalling in a glider, it's routine to fly very close to stall. This minimizes the sink rate, minimizes the turning radius, and maximizes the extracted lift.

I’d hesitate to fly that close (1mph) above stall since the slightest turbulence, which is to be expected in thermic conditions, could lead to a stall or more likely a spin.  In a large thermal it would be typical to fly at minimum sink which will be well above stall speed, or perhaps a little below that to achieve a tighter turn radius to stay in a strong core.

@Frog it all depends on the glider's stall characteristics. Stalls only lead to spins if the plane is badly coordinated, is skidding to the inside, and the stall is not immediately recovered. When I'm flying, I am frequently at the ragged edge 1kt above stall. My glider has very gentle stall characteristics and I respond to the wing buffet within ms of the onset. I certainly understand others flying differently, but my thermalling got much better once I learned not to have a knee-jerk fear of slow flight.

It is possible for any aircraft to fly at one knot above the stall speed and maintain altitude. It does however require a lot of thrust to overcome the induced drag generated from having such a high angle of attack. In a glide, where you don't have to maintain altitude, flying that slow can easily be done. The stall speed represents the point where the wing can no longer fully support the weight, but anything above that is fine.
I wouldn't say it is recommended practice though. Flying so close to the stall is dangerous if you don't have enough altitude to recover. It'll also be uncomfortable for passengers. For perspective, in the PA28 I fly, the stall speed with flaps extended is 44 knots, but we land at 60-65 knots. We also have a "safe slow cruise" configuration which has two stages of flap extended and gives us a speed of about 75 knots. Basically, we don't hang around near the stall speed unless it's for practice.


text:
Is a flight instructor certificate on the same physical card as a pilot certificate?
Are a flight instructor certificate and commercial/airline transport pilot certificate printed on the same physical piece of plastic, or on two different ones?

I can’t speak for other countries, but in the United States, a flight instructor certificate is a separate document from a pilot certificate.  Flight instructor is not a rating which is applied to a pilot certificate. It is an individual laurel with its own privileges and responsibilities separate from a pilot certificate.

While my flight instructor certificate is similar in form factor and coloring to my pilot certificate, it is a different document. The back of it states that the certificate is not valid, unless accompanied by a pilot certificate No. 12345678 and that the document expires 31 August 2024.
It also contains limitations, such as Airplane Single Engine and Airplane Multi-Engine and privileges such as Instrument Airplane.
Other countries may vary from the United States, which is where my certificate(s) are from.


text:
What would happen to a tethered airplane?
Suppose someone attached a mile-long unbreakable rope to the tail of an indestructible airplane in a way that cannot be detached, and the plane takes off and flies in a straight line. The other end of the rope is fastened to the ground at the end of the runway. What happens when the airplane reaches the end of the rope? Does it hover? Crash? Oscillate up and down? Go straight up like a helicopter, if the engine is powerful enough?

If I had to guess it would likely come to a sudden stop, then fall down. The wings need airflow to generate lift.

@At0mic would the airflow from falling suffice to temporarily raise the plane again? That's what I was thinking might cause the oscillation scenario.

I guess one way to find out would be to build a model plane and fly it with a tether.

I think this setup is called a kite and you might enjoy doing the experiment yourself. :)

The airflow from falling would suffice to slow it down like a parachute, for sure not to lift it back (unless there's a strong enough thermic or unless it's a F-35)

Which airplane do you have in mind?

@sophit just a hypothetical airplane; I wasn't thinking of any particular real plane.

Understood, but which kind? A jetliner, a fighter, a propeller, a GA, a glider? Just to do some math

What is the thrust to weight ratio?  Does the pilot pitch up or down at the end of the rope?

@sophit I was thinking of a small propeller plane; if you need a specific model, the Cessna 172 is fine.

Assuming that both the rope and plane are indestructible, the biggest problem in this scenario for the people in the plane is that the rope is attached to the tail. This would rob the crew of any attitude control as long as the rope is taut.
As soon as the plane reaches the end of the rope, it will stop, wings will stop generating lift, since stable planes are nose heavy it will start falling nose first, resulting in airflow over the wings and lift. Had the rope been attached close to the CG, one could stabilize this flight condition and enter an orbit around the other end of the rope.
However since the rope is attached to the tail, the crew does not have any control over their attitude. One trick which could work is to roll to inverted before the rope gets taut, then once in inverted nose down attitude, pull as hard as you can and hope that the nose is heavy enough that you get in a straight vertical attitude before hitting the ground. Then the lift generated by the wing will start pushing you towards the center of the circle, giving the rope a little slack which you could use to pull back to nose towards the horizon.
This is actually a potential accident scenario for winch launched gliders, where a glider connected with a rope attached near the CG to a winch, which pulls the glider into the ait. If for some reason the rope release on the glider is stuck, the winch has an emergency guillotine to cut the rope. Even if that's broken, then the only solution is to enter a decaying orbit around the winch and hope you survive the landing.

This is somewhat speculative b cause there are no unbreakable or indestructible objects, but if we assume that the objects in question won’t break subject to the forces in the experiment, and if we further assume that the elasticity of the rope is. Rey small then the aircraft will quickly come to a stop and will fall parachutally (in this case quite quickly but not in free - fall).  The engines may provide a little airflow over the wings depending on the configuration but it will likely be far from enough to support the aircraft.  If the aircraft is robust enough to withstand the rope then it may well survive the landing.

The ultimate stall!
An airplane needs forward velocity to generate lift.  No matter how powerful its engine is or how much thrust it has, if it does not have forward speed it does not have lift.
Helicopters solve this forward speed issue by spinning its rotor for lift and tilting forward a bit for airspeed.  A airplane cannot do this.
After it stopped, the drag of its structure might limit the speed of its descent, but fall it will because a wing can not support the weight of the aircraft without lift.
What might be more fun is to attach a rope perpendicular to the direction of flight, giving full-scale control line flight.

In reality snapping at the end of a rope would probably cause a structural failure of the airplane, but as we are already working with a massless, infinitely durable rope I'll assume the airplane won't suffer any damage.
The answer depends on where the rope is anchored. Airplanes fly because there's air flowing over the wings, if an airplane was to suddenly stop in mid-air then there would be no airflow to create lift, and the airplane would plummet to the ground. So, if the rope was attached to the tail bad things would happen. If the pilot has enough altitude they might be able to drop the nose and maneuver the airplane back to the airfield, or at least make an emergency landing. Most likely there's a big crunch at the end.
If the rope was attached to the underside of the airplane, or maybe the side, somewhere around the center of lift, then the airplane can still fly. If the rope is on the side the pilot would need to fly a constant turn around the rope's anchor point. If the rope is attached to the underside then the pilot would then have a very strange experience as the airplane would turn around the rope's anchor point, with the wings banked opposite the direction of the turn. In both cases the pilot would need to initiate a turn before the rope becomes fully taut, if not then the airplane comes to a sudden stops and it's crunch time again.


text:
Why does the PA28 only have one door?
I did the majority of my PPL training in a PA28 Warrior and I've recently started transitioning over to a C172 and one thing that amazes me is how convenient it is to have a door either side of the aircraft.
My question is: Why does the PA28 only have one door on the passenger side of the aircraft?
I've never seen the schematics of a PA28 but my assumption might be that there's equipment that runs down the left side of the fuselage preventing a door from being added.

I don't have a good answer for this and I'd love to have one!

Good question, and my one main criticism of an otherwise lovely aircraft. What's worse, is that it's the Pilot who doesn't get a door meaning your poor, nervous, first time passenger now has to climb in unaided and take "responsibility" (real or imagined) for closing the door.

The difference in door design also makes It a little quieter and less traumatizing for passengers.  I can't count the number of times a door has popped open in a rental Cessna.  Don't recall it ever happening in a Piper style door.

This is pretty common with low-wing single engine GA aircraft

Having one door is just a design preference which makes the aircraft simpler, and lighter to build.
There are many other light aircraft with only one door. Besides Piper, most Mooney, Beechcraft, and Bellanca aircraft only have one door. Even the high wing Cessna 195, 206, P210, 337, and low wing Cessna 310 and 340 have only one door.

Not a criticism, I would like to see some citations though. There's a lot of speculation out there.

Good observations but I was hoping for something with some citations like @GdD mentions.

Ignoring the structural considerations, it seems to be common sense that if you put a door in you'll need hinges, door seals, latch mechanism, cost of cutting a giant hole in the metal and installing all the pieces, ongoing adjustment and safety inspections...

@GdD, the Citation has two doors.

@Mark, "GdD" was referring to a citation as a reference to a published or unpublished source.  I don't have any citations and I don't feel they are needed as it is very obvious that additional doors add add weight and complexity to any aircraft design. ALSO.... Cessna Citation's have ONE entry door and an emergency exit which really can't be called a door.

@MikeSowsun, I know, but the pun was too good to resist.

Good one  ;)    ....

I realize this is an old feed, but I'm still wondering: Sure, there are structural, weight and complexity concerns that justify one door versus two. But, why is the passenger side the selected side? A pilot side door seems much more convenient for ingress/egress during single pilot operations.

@Geoff traditionally the captain welcomes his passengers on board of a ship or aircraft and bids them farewell as they leave, himself being the last to leave. That may be a big part of it.

@Geoff I'm the pilot of an airplane with one door on my side. I wish to drop off the passenger sitting to my right without shutting down the engine. Very inconvenient having a male crawling over me to get out. Now, on the other hand, if the pax is a good looking young woman, that might be the way to go (feel free to reverse genders according to preference). Seriously, when the PA-28 and others were designed, It was not uncommon to load/unload pax with the engine running. I did it many times. Unsafe you say? By today's standards, yes; by 1970's standards, no.

Mike, do you have any citations that the aircraft you mention ... are actually aircraft?  :)

It reduces weight and increases the structural strength of the fuselage, particularly with the typical design of a low wing aircraft.  Later low wing aircraft like the Cirrus make use of an internal crash rollcage in the dorsal spins of the fuselage which adds extra strength to accommodate the second door.  Diamond uses a semi monocoque tub-like design with a single swing up canopy enclosure to facilitate ease of entrance and egress.

Piper's early low wing plane history, the best info I have found has been this:
http://www.pilotfriend.com/aircraft%20performance/Piper/11.htm

In 1954, Bill Piper was looking for a design to compete with the Bonanza. The engineers at Piper were busy with other projects at the time, so Bill Piper asked his friend Al Mooney if Piper could buy the new Mooney MK-20 design that Mooney had not yet started producing. Al wouldn't sell the design, so Bill Piper asked Al Mooney to come up with a totally new design. Al submitted a design to Piper that was an all metal 4 place monocoque construction with retractable gear, a 180 HP Lycoming, and a stabilator in place of an elevator. The stabilator was a new design, an all flying horizontal tail.
The cabin size of Al Mooney's design was a bit small, so the engineers at Piper increased the cabin size and the first Prototype PA-24, N2024P, was created in 1956. As you can see in this photo, the trailing link landing gear on the prototype is not what we have on our Comanches. It is suspected that Bill Piper decided that the trailing link landing gear would be too complex and expensive, and in an effort to undercut the cost of the Bonanza, he decided on the straight tube oleo strut landing gear that all Comanches are equipped with. Although it is much more difficult to make a good landing with the straight oleo strut landing gear than with the trailing link gear, that decision by Bill Piper is why Comanche Pilots have skills much more superior and a highly qualified group of Pilots than the Bonanza and Mooney bunch!!
The second prototype PA-24-180 flew in 1957. The first production 180 was delivered in January of 1958. It cost $14,500. The 250 HP Lycoming was meanwhile being tested in the original prototype PA-24, and the first production 250 Comanche was delivered in April of 1958.

And from Wikipedia:

Piper PA-28 CherokeeI have
At the time of the Cherokee's introduction, Piper's primary single-engined, all-metal aircraft was the Piper PA-24 Comanche, a larger, faster aircraft with retractable landing gear and a constant-speed propeller. Karl Bergey,[12] Fred Weick and John Thorp designed the Cherokee as a less expensive alternative to the Comanche, with lower manufacturing and parts costs to compete with the Cessna 172, although some later Cherokees also featured retractable gear and constant-speed propellers.

could you highlight the parts of those quotes that answer the question "Why does the PA28 only have one door?"

Thought that was obvious - because they were copying what other companies had already done.

sorry, didn't mean that. yes, in a sense it is obvious, but it is still better to either highlight specific sentences or to provide a summary in the answer, particularly for such extensive use of quotes

One could also try this link to the history of the development of the Bonanza Model 35  http://www.airbum.com/articles/ArticleBonanzaGuide.html  or this link to the Bonanza society  https://www.bonanza.org/

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why is a contra-rotating High Pressure section more efficient?
In the Rolls Royce Trent 900 marketing material, the use of contra-rotating HP system is described as increasing the efficiency of the engine. Can anyone explain why/how that increases the efficiency?

These marketing type documents don't always mean "efficiency" in the true technical definition of the word, nor is it clear if they are talking about turbine stage efficiency (i.e. efficiency of the nozzle/turbine blade expansion process), or overall engine thermal efficiency.
The main advantage of contra-rotating is the removal of the nozzle guide vanes (NGVs) between the high pressure turbine and low pressure turbine. These LPT inlet nozzles require cooling air, that needs to be from a reasonably high pressure source because it has to be at a higher pressure than where it is being introduced back into the hot gas stream. Hence, it is usually bleed from within the high pressure compressor exit. (See reference below to "HPC S7 Air" - which means stage 7, this is the GE90 engine which has 9 or 10 HPC stages depending on the model).
In comparision, HPT inlet nozzle guide vane cooling air has to be bleed from the HPC exit, as an even higher pressure is needed. (see reference to "HPC exit air", or "CDP", compressor discharge pressure).
(Pic from here)

Given the LPT nozzle guide vanes require cooling, removing them reduces the cooling air required, and hence this air, which has been compressed which required turbine energy to do so, and hence represents an energy investment by the engine, is still available in the combustor, and for extracting (recovering) work from in the high pressure turbine. Therefore, the thermodymanic cycle efficiency of the engine is increased, as parasitic cooling air requirements have decreased.

In addition to bleed air energy savings, there is the simple business of taking energy out of the guide vane - as the counter rotating disc now performs that function - and putting into a shaft driving the high pressure compressor section, that is also conter-rotating and eliminating the induced drag of the "lift" produced by one stage of guide vanes at that end.  I believe there are still guide vanes between the second stage compressor and the high pressure compressor, as well as between the first turbine disc and the second stage section at the hot end, but these will be more axial in alignment, thus two interfaces let the energy of re-directing what would have been a helical flow in "normal" engines instead power a shaft instead of just pushing torsionally against the shell of the engine.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is the rate of acceleration based on downward pitch?
In other words, I want to understand how gravity converts into thrust in respect to pitch. What is the general mathematical relationship? (For visuals, imagine a bird diving to gain speed.)

Related (to falcon dive): Gliding flight: speed and acceleration of ideal falcons during diving and pull out

Assuming this is the standard inclined plane task from physics textbook, as here for instance, the acceleration is
$a = g \cdot \sin(\theta)$
where $a$ is acceleration, $g$ is the free fall acceleration (9.8 m/s^2) and $\theta$ is the pitch angle down (0 assuming horizontal).
This equation applies does not take the air resistance into consideration so would only apply to relatively slow speeds. The equation also assumes that the plane orientation matches the flight direction, this is obviously simplification.
Interestingly, under these conditions the acceleration does not depend on the mass of the plane. The equation should also apply for the positive pitch angles, but the acceleration would be negative in this case (slowing down).


text:
is nitrogen put in airplane tires? and Why?
I now the A12 and sr 71 had nitro in tires, but thats extreme. what are the beginning factors that dictate what is put in the tires?

Related-- https://aviation.stackexchange.com/questions/64682/does-nitrogen-inside-commercial-airliner-wheels-prevent-blowouts-on-touchdown --see several answers

Why would that be "extreme"? You can get nitrogen put in your regular car tires at many mechanic shops.

@HiddenWindshield -- I suspect the questioner meant not that using nitrogen was extreme, but that the A-12 and SR-71 represented extreme cases in terms of the demands imposed on tires.

I use at least 78% nitrogen in my car's tires, and I think you should too.

Transport airplanes use dry (completely dehumidified) nitrogen from high pressure bottles for tire servicing. Shop air is "dehumidified" using water separators but will still have water vapour in it. Bottled dry nitrogen is completely moisture free.
Besides humidity, the main objective is removal of oxygen. Oxygen, the other major element in air at 21%, tends to oxidize the rubber, degrading it.
So using dry nitrogen eliminates humidity related problems and eliminates internal oxidation of the rubber (as well as making the inside atmosphere completely incombustible), so it's generally the standard for commercial aircraft where the tires run at extreme pressures and speeds.
Light airplanes will use dry nitrogen if it's available and the owner wants to go to the expense, or just regular shop air as you would a car.

Although oxygen molecules are smaller than nitrogen (0.299 vs 0.305nm) the difference is insignificant from a leakage perspective.  That’s nanometers of course, not nautical miles

Thermal expansion coefficient of oxygen and nitrogen should be basically the same i.e. like the one of any other (ideal) gas. I suppose that the main reason to use pure nitrogen instead of air is still to avoid to feed any fire in case of incident.

@Frog even at 150-200 psi?

@sophit I thought there were small differences at higher pressures no?

@sophit Air does not behave as an ideal gas due to the presence of water vapor. Water has a strong dipole moment, which makes it deviate from an ideal gas, particularly as the tire is expected to operate within the relatively small range between freezing and boiling of water.

@user71659: yes sure, water is not an ideal gas. But the answer is speaking about the expansion of oxygen vs. nitrogen.

Nitrogen has a lot of benefits when used in tyres, not just in aircraft but in cars, trucks, motorbikes and so on.
First consider the alternative. If you fill the tyre with air you will get some water vapour, exactly how much depends on the humidity at the time. Water density varies between 0.6Kg/m3 to 997Kg/m3 over just 100 degrees C. That results in a big change of pressure from even a small amount of water. Air has many other things in it as well, including oxygen which supports combustion and hydrogen which leaks out reducing pressure. Nitrogen is cheap and it is boring. The molecules are all the same size so there are no leaks, it doesn't burn in an accident and the pressure remains linear with temperature. If you have the option, and most places that do a lot with tyres do have the option, then using nitrogen is a cheap and effective solution for managing tyres.

I'm not sure this answer presents a balanced viewpoint when it comes to road vehicles. Most objective, independent studies show no more than negligible benefits for cars, making the whole thing a marketing gimmick. It is correct that nitrogen is used in aircraft tires with benefits arising from the high temperatures reached.

@TypeIA The issue is how much O2 remains in tires. Car garages generate N2 on-site from molecular sieves, which still are 2-5% O2. Further, the tire isn't flushed and often topped off with air, making the ratio even worse. Airplanes use N2 from suppliers that are better than 99.9%.

"The molecules are all the same size so there are no leaks". I think that also the molecules of oxygen have all the same size. Why should it have an impact on leaking?

The leak rate has only quite remote connection with the molecule size. The important thing is how much the corresponding gas is soluble in rubber. And the oxygen is indeed much more soluble..

@TypeIA - Road cars do not significantly benefit from nitrogen because road cars do not tend to experience extremes and a difference in pressure of 20% from optimum can rarely be detected by the majority of drivers. Race cars and motorbikes are much more sensitive to pressure and so the benefit is greater.


text:
Are right hand patterns allowed at any airport with approval?
I noticed a GA plane fly pretty low over my house today heading towards PDX. I checked on FlightRadar and noticed it made (what seemed like) an unusual maneuver. It flew directly to the airport and entered what looked like a very abbreviated right hand pattern to runway 10 at only a few hundred ft MSL. I think it was a touch and go, and it took off right afterwards. The sectional doesn’t show a RP for any PDX runway, and it doesn’t really match any IFR approaches either. What might this be and when would it be approved? I didn’t take a screenshot of the flight path so I recreated it.

There's just not enough space on a sectional chart to list all the same details as you would see at a small airport when there are multiple runways.

Generally at 5-6pm PDX gets about 8-10 Cessna 208s, Fedex feeders, headed northbound. If traffic and winds allow, they land on 3 (northbound). One did a loop over North Portland (CFS7690) onto 3, another looped onto 10R (AMF1985), a few did an abbreviated pattern that matches your drawing (CFS7675, AMF1967), but they landed on 3 and 10R. APC1911 took an interesting path.

What time was it that this happened? There is a good chance we can go back and look at the ADS-B track of the specific plane, and then possibly even get the audio of ATC around then, and concretely find the ATC instructions to that plane!

When you're at a controlled airport, ATC directions can be anything they want for pattern entry.
AIM 4-3-2 does a poor job of saying it with this text:

When necessary, the tower controller will issue clearances or other information for aircraft to generally follow the desired flight path (traffic patterns) when flying in Class B, Class C, and Class D surface areas and the proper taxi routes when operating on the ground. If not otherwise authorized or directed by the tower, pilots of fixed-wing aircraft approaching to land must circle the airport to the left.

But this example would likely be an ATC instruction to make right traffic.

Just as a useful example - KRNT does this a lot. KRNT is normally a left pattern for 34, but I have been given clearance to enter right base for 34 many times because when coming from KBFI, it makes a lot more sense and fits in better.


text:
optimal airplane propeller placement along the vertical axis?
is there a guideline for optimizing flight based on where the engine/propeller is placed along the vertical axis?  some planes have the propellers well below the wings, some on the wings, some above the wings.
i've been reading about center of mass, center of lift, center of pressure, and center of thrust, and none of these seem to address this.
is there any sort of "center of drag" concept?  so like if i'm quickly pulling a plane horizontally through the air on a string, the point of string attachment where the wings will be level to the ground?  eg if i had a plane with a very tall fuselage that was completely under the wings, and attached the propellers to the wings, i'm assuming the plane would have a tendency to nose-dive due all the drag pushing against the front of the fuselage under the propeller/(thrust vector). ?
namely, will the bottom 2 planes, below, have a tendency to lurch forward/downward because of this (unlike the top plane)? something that would have to be counteracted by the tail and be less efficient because of it?

The vertical placement of the thrust line (relative to the aircraft's CG) will determine whether the engines make a positive, neutral, or negative contribution to the pitching moment.  This contribution to moment will vary with thrust - and potentially abruptly in the case of an engine failure.
The similar contribution of drag gets resolved into the overall pitching moment of the aircraft.  But certainly, retracting the landing gear (mostly a drag change) can change this moment (for example).
Many aircraft are designed with a preference to place the thrust line running through the vertical location of the CG to neutralize this contribution to the moment.  However, the moment arm of the thrust line (to the CG) is relatively short (say compared to the distance from the CG to the horizontal tail) and this contribution to moment is at best a second order effect.
Consequently, if aircraft have a good reason to place the engines high or low (as compared to the CG), they will probably do so for that good reason -- and will then work to resolve whatever penalties are caused by this contribution to moment.


text:
Help me identify this GA twin engine aircraft
Apologies for the quality.
Other snippets from the video show wingtip tanks, but these could be a mod.
The most distinctive thing about it that I can see it the side window

This may be the same aircraft, but can't guarantee it

what/where is the video?

The video isn't aviation related, the plane appearred for just a few seconds, the only decent stills from it are here.

The aircraft is a 1971-1976 Cessna 421B. Here is why:
The pilot side window vent identifiers this as a pressurized Cessna 400 series which means Cessna 414 or Cessna 421.
The Propellor hub looks like it has a higher thrust line, and is attached to a geared engine, which means it has to be a Cessna 421. If the engine is not geared, it may be a Cessna 414.
The tip tanks are stock Cessna tanks. Which came on many models.
The long nose narrows it down to a Cessna 421B because the Cessna 414 with tip tanks had a short nose. The Cessna 421B was manufactured from 1971 to 1976.
Wikipedia Cessna 421B photo

Those geared engines are run sooooo hard.

Superb answer. Thanks for sharing the reasoning behind it

I swear that triangular window looks like a "wing window," common in cars of the era.  I know it's not one, but still.


text:
Unstable Approach
What is considered to be an "unstable approach"?
Which are the exact parameters against which an approach is being judged, in order to be considered "stable" or "unstable"?

Does this question help?

The exact criteria varies amongst aircraft type and even from airline to airline.

Does this answer your question? What is a stabilized approach?

For visual landings, when you gain experience and skill, the need for a "stable" approach all the way down to be able to land safely becomes somewhat less important, as long as you can get yourself configured properly in the last couple hundred feet. When you get to that "at one with the plane" level of skill, that can be fairly easy to do.


text:
How does one resume a VNAV climb in a B737 NG after being instructed to level off at an altitude below the Cruise altitude?
I am referring to a Boeing 737NG.
Assuming I am on a VNAV climb but I am instructed by ATC to climb only to an altitude lower than my FMC Cruise altitude.
After leveling off, how do I resume my VNAV climb to my FMC Cruise altitude after I am cleared by ATC to do so?
I obviously have to set my FMC Cruise altitude in the MCP Altitude window, but as VNAV is already engaged from before ans is the active mode, will the aircraft start climbing automatically, or do I have to disengage and re-engage VNAV by pushing the VNAV button OFF and ON again?
Or, alternatively, do I have to press the ALT INTV button to resume the VNAV climb to my FMC Cruise altitude?

Turn off autopilot, push thrust lever forward, pull back on yoke, at FL410 turn on autopilot.

So your CRZ page shows your cruise altitude as FL 410, but you've leveled off at FL370, which is what's in your MCP Altitude window. Now ATC clears you to climb to 410.
You set 41,000' into the MCP Altitude window. At this point, your FMA vertical mode changes from VNAV to Altitude Hold. The light in the Alt Hold button is on, and the light in the VNAV button is not. To initiate the climb, press the VNAV button, and observe the FMA change from ALT HOLD to VNAV Speed. At this point, the autothrottles advance the power, the autopilot increases the pitch to maintain your FMC-computed airspeed, and you're climbing again.
The key is that when you initially leveled off at FL370, the FMA stayed in VNAV Speed, but as soon as you changed the MCP Altitude, the FMA changed to Altitude Hold. Thus, one tap on the VNAV button re-engages VNAV & you resume the climb.
Side note: why doesn't the FMA change immediately to Alt Hold when you level off at 370? While Boeing may have another answer, my best explanation is that if you change your cruise altitude in the FMC from FL 410 to FL 370 after you leveled at 370, you stay in VNAV, and the FMA just swaps from VNAV Speed (i.e. the climb mode) to VNAV Path (i.e. level-at-cruise-altitude mode). So at the intermediate level-off, it stays in VNAV, waiting to see if you'll reset the MCP altitude (to continue the climb) or if you'll reset the FMC cruise altitude (to make this your cruise altitude). In the former case, the VNAV button starts the climb; in that latter case, no MCP buttons need pressing.
Added:
The case where Altitude Intervention will start your climb is different: in that case, you're AT your FMC cruise altitude, either because you climbed there directly, or else you leveled off at an intermediate altitude and then changed your FMC cruise altitude to match.  The latter is NOT common practice, but there are scenarios where it could happen.
Either way, you're at cruise in VNAV Path.  Now ATC clears you higher.  So you set the new, higher altitude in the MCP altitude window.  At this point, the FMA still displays VNAV Path.  Press Altitude Intervention, and that changes the FMC cruise altitude to what's in the MCP.  With VNAV (still) engaged and your altitude below both the MCP altitude and the FMC cruise altitude, you'll get a climb.
The difference in these two cases is being at, or not being at, the FMC cruise altitude.  In the case discussed first, you're below it.  In the second case, you're at the cruise altitude.  In the first case, Altitude Intervention won't help you (because you're in ALT HOLD and not VNAV); pressing VNAV will.  In the second case, you're in VNAV, so pressing that button won't help you; resetting the FMC Cruise Altitude (either by entering it in the FMC via the CDU, or by pressing ALT INTV) will.
This stuff is complicated, and the manual doesn't generally do a great job walking through every scenario and "what if".  After you've seen it in the jet (or a simulator with good fidelity) a few (dozen) times, it makes much better sense.
I'm not aware of any 737 setup where anything varies varies from what I've discussed above, although if the Smiths FMC is replaced by something else, all bets are off.  There are some things that vary from one aircraft to the next (geometric path descent vs idle descent logic being one -- it's selectable by the airline), but nothing here, as far as I know, is in that category.
As far as simulators go, I can't speak to which ones have fidelity to what goes on in the real aircraft or not.  (The ones I train in are extremely accurate that way, but they're not running on a PC!)

It seems that there are varying software and it all depends on the specific FMC/MCP hardware installed.
See below:

ps://i.sstatic.net/iB5Bp.jpg

The Alt Intv function addressed at the red bracket works when you are AT your FMC Cruise altitude & you've dialed a higher altitude into the MCP. That isn't the scenario the OP asked about. Also, nothing on these pages supports the "varying software/specific hardware" statement with regard to anything in the OP's question.

Oh, wait, you ARE the OP.  In your original question, you leveled off BELOW the FMC cruise altitude, yes? And didn't change the cruise altitude to match, presumably. (You'd affect fuel predictions if you did that.) In that case, Altitude Intervention won't help you.

Also, nothing on these pages supports the "varying software/specific hardware"
In the first answer, dialing a higher altitude the MCP switches from VNAV to ALT HOLD. In the other case, no mention of ALT HOLD is mentioned. In the first answer, you resume climb by re-engaging VNAV. In the manual I posted above, you resume climb by pressing ALT INTV.
Or have I got it wrong? (quite possible :-) )

I've added an explanation to my answer to address how the system works.  The manual posted is entirely consistent with what I'm describing, but there are two different scenarios -- one needs VNAV, the other needs the FMC Cruise Altitude changed (via ALT INTV or otherwise).


text:
How to deal with both a speed and an altitude crossing restriction while in VNAV PTH descent (Boeing 737NG)?
Suppose you are in VNAV PTH descent and are approaching the IAF for your Approach, The IAF has both an altitude crossing restriction and a speed restriction.
Assume that your VNAV PTH descent is at 240 kt at that moment and the speed restriction is 210 kt.

Will VNAV automatically "see" the speed restriction and reduce the descent rate (pitch up) to meet the lower speed? If yes, won't it then miss the altitude crossing restriction, as the planned path is modified?

If the PIC uses SPD INTV to set the limiting speed, won't VNAV switch to VNAV SPD and thus once again automatically pitch up to reduce the speed? Again, this may result in not meeting the altitude restriction, as you will end up higher than your intended path.

So, the question is, what should you do in a situation like this?
My guess is, revert to V/S and MCP SPD, use Speed Brakes and arrange to be over the IAF at the correct speed and altitude, and then re-engage VNAV.

With both restrictions entered on the LEGS page, VNAV will build a deceleration segment immediately prior to the point to reduce speed from 240 to 210 knots in (almost) level flight. There is no need, typically, to come out of VNAV, use the speed brakes, or do anything else like that in order to have VNAV meet both speed & altitude constraints.
Thus, the Top of Descent point will be about 3 miles sooner for a restriction to "cross XYZ at 9,000' & 210 knots" than it would be to "cross XYZ at 9,000' & 240 knots". It takes about 1 NM to slow 10 knots in level flight at idle.
The exception to not needing to come out of VNAV is if you end up with excess energy - perhaps unexpected tailwinds. In that case, you have to lose the energy, which is most easily done with the speedbrake. Switching between modes doesn't bleed energy, although it may affect the tradeoff between kinetic & potential energy. (If you have enough distance, using Speed Intervention to increase speed CAN bleed off excess energy by increasing drag. BUT, you then have a longer decel segment... so to gain from this you either have to spend several minutes at the higher speed, or be descending to a point with only an altitude restriction, but no associated speed.)

"using Speed Intervention to increase speed" I assume you meant to write "decrease speed"?

"VNAV will build a deceleration segment immediately prior to the point to reduce speed from 240 to 210 knots in (almost) level flight." So it will have taken the speed reduction into consideration, when defining the T/D and bring it a bit forward than otherwise?

@StamatisVellis. "...to increase speed" is correct - it's about bleeding off excess energy, and higher speed = higher drag = more energy dissipated. Slowing early typically exacerbates a high-energy state.

I am confused with the "to increase speed" part, because we are looking to decrease speed, not increase it in the case examined.

The answer above is largely a complete one.  I would only adf a couple of small details.  FMC computations determining where to set the path are more accurate if winds aloft are entered for multiple levels on the descent forecast page.
As to speeding up or slowing down to manage energy, you would need to consider the descent airspeed in relation to where the aircraft is most efficient.  The 737-NG comes down like a leaf at 270 knots +/- a few depending on weight.  Cost index is a factor here too.  Waiting until the last minute before diving down at 320 knots would provide a higher groundspeed and save time to the destination.  The dive also requires planning to include a period of deceleration prior to the crossing restriction.  Ten knots per mile works in level flight; you need more if decelerating in a descent.  Calculate based on knots of groundspeed...
The mental calcs are good for situational awareness, but the FMC manages the path and speed nicely if you program the winds.

Fully agree. Welcome to Av.SE!


text:
What are the conditions under which one would normally switch on the Engine and the Wing Anti Ice?
As per the title. But I would also like to know if both (Engine and Wing) are turned on at the same time or if different conditions dictate the use of each one. I am specifically interested in the case for the B737NG.

@JohnK this is the comments. Please use the answer box for answers. Comments are to seek clarification on the question and very little else.

@JohnK Then please don't post it.

In general the cowls get operated way more than the wings, because the operating requirements are more stringent, because ice can form on cowl inlets more readily than the wings in conditions near freezing (temperature drop from inlet flow) and the consequences can be worse when the ice is shed.
Can't speak for the 737, but on the CRJs at least, the cowls have to be on in conditions where the wings don't, such as flying in visible moisture above 230 kts (above which the wings only have to be on if you get an actual detection of ice on the airframe).  So when you depart in real icing or "technical icing" (visible moisture below a certain temperature) conditions, both wings and cowls will be on, but during the enroute climb you don't need the wings on without an ICE caution message, whereas you still have to put the cowls on pretty much any time you are in cloud.
In the CRJ program the duty cycle of the cowl AI system was several times higher than the wing AI system because of this, and I'm sure most airliners are similar.

The Boeing 737 FCOM agrees quite well with the procedures John K showed for the CRJ:

Engine anti-ice should be on when flying in icing conditions.
Wing anti-ice should only be turned on when actual icing has been detected.

Engine Anti-Ice Operation - In-flight
Engine anti–ice must be ON during all flight operations when icing
conditions exist or are anticipated, except during climb and cruise when
the temperature is below -40°C SAT. Engine anti–ice must be ON before,
and during descent in all icing conditions, including temperatures below
-40°C SAT. [...]
Wing Anti-ice Operation - In-Flight
Ice accumulation on the flight deck window frames, windshield center
post, or on the windshield wiper arm may be used as an indication of
structural icing conditions and the need to turn on wing anti-ice.
The wing anti-ice system may be used as a de-icer or anti-icer in flight
only. The primary method is to use it as a de-icer by allowing ice to
accumulate before turning wing anti-ice on. [...]

(Boeing 737 NG FCOMv1 SP.16.9 - Supplementary Procedures - Adverse Weather)


text:
Referring to the B737NG, at what point (height) does a TOGA revert to LVL CHG after the takeoff?
If one takes off with HDG SEL armed and no vertical mode (like VNAV) armed, at what height (AGL) will the vertical mode switch from TOGA to LVL CHG, and what will be the IAS applied?
Also, why isn't it possible to arm LVL CHG before takeoff, as it is with VNAV?
Depending on the entered plan, there are instances when VNAV cannot be armed, even if one wanted to.

LNAV & VNAV can be armed before takeoff; HDG SEL cannot be similarly armed.
If VNAV is armed & LNAV is not, then when VNAV engages at 400', the lateral mode switches to HDG SEL. But that's because the pilots had armed VNAV.
Taking off in TO/GA, the system won't revert on its own to LVL CHG. You can climb into the flight levels still in TOGA, although it's hard to think of a good reason to do do. If TOGA is active when the autopilot is engaged, the vertical mode will change at that point to LVL CHG, with V2 + 20 as the commanded airspeed.
As to why there is no option to arm LVL CHG on the ground, there is no need to. TOGA gives you speed guidance to bugged speeds (starting with V2 + 20) anyway, and VNAV gives you guidance to the profile speeds. Why offer another mode change that adds nothing to what you already have?

"If VNAV is armed & LNAV is not, then when VNAV engages at 400', the lateral mode switches to HDG SEL."
I believed HDG SEL becomes active the instant TOGA is engaged, before the takeoff. Not at 400'
"You can climb into the flight levels still in TOGA" Are you sure about that? I believe TOGA changes automatically to MCP SPD when CMD is engaged.

TOGA commands wings level, NOT a turn toward the heading bug (which is what HDG SEL would command. As I wrote, TOGA switches to LVL CHG when the A/P is engaged (in CMD), but you could hand fly it up to FL410 and TOGA wouldn't change to LVL CHG on its own.

Well, I am not a pilot, just an enthusiast. But in the B737-800 FCOM of Boeing that I have, under Automatic Flight Takeoff Profile, it shows all the FMA stages during takeoff and it clearly shows HDG SEL for the lateral mode, starting from the stage "Push TOGA switch", before beginning the takeoff roll, until "Engage AP", after Thrust Reduction. This is what I mean by HDG SEL, the lateral mode used. If I new how to upload the page, I would.

If you set the heading bug well off of runway heading & push TOGA & take off, the FD will command a wings level straight  ahead track. It will only command a turn to the selected (bugged) heading when HDG SEL becomes active, either by pushing the HDG SEL (or LVL CHG, iirc) button or VNAV becoming active. Without seeing the page you're looking at, I can't address what you're seeing, but what I'm describing is how the planes that I fly do work.


text:
What should the back of my pilot certificate say?
I hold an ATP multi engine land rating, as well as a commercial single and multi. But the back of my card says
Airline Transport Pilot
Airplane Multiengine land
Commercial Privileges
Airplane single engine land
Is this right? Should it not say multi and single engine privileges?

Yes.  The back of the certificate is correct.  The AMEL moves to the ATP line and the ASEL stays on the Commercial line.  There is no instrument airplane rating as that is removed with the addition of the ATP certificate.
The ATP AMEL stipulates that you can use it for both airline transport and commercial pilot privileges.


text:
According to which rule, the maritime patrol aircraft are categorized?
Generally, maritime patrol missions are conducted by several types of fixed wing and rotor wing aircraft according to its endurance, capabilities and other features such as weapons, sensors surveillance payload onboard aircraft. Each aircraft is selected for a mission considering above facts. I want to know that, is there an international rule or guideline to follow when selecting the particular aircraft?

What sort of rule, and why might there be an international rule?  (You highlighted some good criteria)

It would not make any sense to have an “International” rule or guideline. Each country’s requirements would be different  to satisfy their own needs.

There is no such rule. A country uses what resources it has, to meet the desired mission. It makes no sense for Mexico or South Africa to consider "rules" for a MQ-4C Triton, because they do not have any.

As a military aircraft, they are regulated under FAA Chapter "get outta here, civilian, or I'll call Shore Patrol and have you arrested for trespassing".
In other words, it's military, so anything goes.
If an aircraft can fly and is fit for mission, or even if it's not, by golly it can be in the air. Indeed, the lowly Antonov-2 cropduster has been used for the most absurd things - insurgency operations, COIN operations, tactical airlifter, and Russia has gathered about fifty they're planning to use as drones to try to saturate Ukraine air defense.   Come to it, it would make a first-rate maritime patrol aircraft, being able to carry the huge Mk. 48 anti-large-ship torpedo, and about six of the small Mk. 50 ASW torps....
... except for the problem that most submarines could outrun the Antonov-2 :)

I think the slightly more formal name for the chapter you're referring to is "due regard."  Which isn't strictly an FAA thing, but part of international conventions.


text:
Why do vapour cones appear for such short periods of time?
Is it just because the air they are going through is more humid than the surrounding air so when they leave that patch the cone disappears?

How are condensation cones created by supersonic airplanes?

You'll want to check out NASA SP-514.  In particular Chapter 2.
The vapor cone you see is actually a cloud.  It is condensation of vapor into tiny water droplets when the temperature and pressure are just right (based on the local humidity).
So, changes can occur due to local changes in humidity and temperature -- but the biggest effect is changes in pressure due to the aircraft.  For example, sometimes the condensation only occurs when the aircraft is "pulling g's" -- it is highly loaded during a turn or other maneuver.  During this state, the aerodynamics are working hard -- which leads to more extremes of pressure and a greater likelihood of condensation happening.  However, the pilot doesn't sustain that maneuver for a long period, even relaxing a slight amount can make the condensation vanish.

Also note that the precise conditions required to produce a cone cloud of condensate right behind a shock front are transient- they disappear quickly after the shock passes as the ambient air strives to come back into pressure and temperature equilibrium.


text:
Conversion of downward velocity to forwards velocity?
When a plane dives down and then pulls up (assuming that the plane is not in a stall), how exactly does the plane keep its speed when leveling out?

By adding power?  Not sure what you mean otherwise...  (if a skateboarder drops down a ramp onto level pavement how does he keep his speed?)

Yes, throttle control.  "When a plane climbs and levels out, how does it prevent its self from going too fast" would be a corollary.  Gliders do speed control by adjusting pitch angle relative to the ground (gravity is the "throttle").

For most airplanes, lift is an order of magnitude higher than drag. This means that lift acts in a direction not exactly, but mostly, orthogonal to the direction of movement and an axis parallel to wingspan.
Lift is normally created to oppose gravity so the plane stays aloft. However, during maneuvering, the pilot will point the lift vector into the newly desired direction of flight. This is done by both changing the magnitude of the lift vector and the attitude of the airplane.
Consider a turn: The pilot will roll the airplane such that the lift vector  now points partially sideways into the desired direction. Also, by changing the magnitude, the pilot ensures that enough lift is left pointing up so the airplane can maintain its altitude. Now the sideways component of lift will pull the airplane into the new direction and also decelerate it in the old direction.
In a dive and subsequent pull-up, the same happens, only in the vertical plane.

Glider in a pull-up. Own work, DFS Habicht by Wolfram Gothe (source).
Note how initially lift will accelerate the airplane horizontally, so it becomes faster as it dives down, and on the upward path will decelerate it so it slows down again. All the time, lift will also pull the airplane into the circular movement by being larger than gravitational acceleration.
Also, the slight backward tilt of the lift vector relative to the longitudinal axis of the plane will make sure that it will not climb as high as from where it started the dive. Thrust will be needed to compensate for this backward tilt which we call drag.

The lift in all of your pictures is directed a little more than 90 degrees from the flight path. Then, in all three situations it is slowing the glider down. In a dive, it's the weight that acts in a direction to speed up the glider, not the lift.

@Chris however, the lift vector does help it accelerate it in a new direction.  "Pulling out" of a dive involves a  change in flight path.

@RobertDiGiovanni Yes, it changes the direction. With the typical definition, it doesn't speed it up or slow it down. If you include "induced drag" in the definition of lift it also slows it down a bit always.

@Chris Did you notice the word "horizontally" that comes with accelerate? At the bottom of the maneuver the airplane is faster and that speed does not come from gravity. I might need to remind you that gravity only acts in the vertical direction. It can only give the plane a downward speed component.

@PeterKämpf Horizontal velocity or momentum component would make sense. At every point, the lift is acting to slow the instantaneous speed (and also to change the direction of the velocity vector). The speed/kinetic energy comes solely from gravity- if you imagine "turning off" gravity while keeping the other forces constant, I'm sure you agree that the glider cannot in any way gain speed, yes?

@Chris So in a turn it is gravity which makes an airplane change direction? This does not make sense. Please reconsider. Start here: Speed is a vector, not a scalar!

@PeterKämpf Speed is a scalar, velocity is a vector. Lift makes an airplane change direction (so can gravity, of course- that's essentially what happens in a stall), but it never makes it faster. By diving, a glider can gain speed (gravity does work on the glider), and then it can use its lift to change the direction of its velocity. If lift was directly causing the glider to gain speed, one would expect that pulling sharply up, and thus dramatically increasing lift, would cause a sudden large increase in speed. This, of course, is the opposite of what happens.

@Chris Now I understand your nitpicking. It is the wrong word that I used, not the wrong physics.

@PeterKämpf The wrong word, but also the wrong physics. Forces pointed "backwards" relative to the direction of motion simply do not speed things up. Draw the free body diagram along with the direction of motion of a glider in a dive. Compute the work done by each force. It will be negative or zero for lift (depending on your definition of lift), negative for drag, and positive for gravity.

@Chris This is my last comment. You seem to have forgotten what the question is about. It even uses your preferred terminology, so it should be straightforward to understand.

In order to pull out of a dive, the pilot has to pull back and pitch up the aircraft. This increases the angle of attack, and thus the lift. This acts in a direction perpendicular to the flight path, and so acts to change the aircraft's direction without affecting its speed much.
It also may increase the drag somewhat, which will cause the speed to slow somewhat. And, of course, once the aircraft is in level flight its speed will change if the thrust is insufficient or too much to maintain unaccelerated flight.


text:
Elevator / horizontal tail effectiveness at high speeds?
Take for example a jet fighter, when at low speeds vs high speeds, airspeed will differ a lot. As the turning moment is due to the lift force from the tail and lift increases quadratically with airspeed, why doesn't the jet fall out of control at such high speeds. To give an example, take a jet flying at 300 kts vs 1000kts. That means that the faster jet will have a turning moment 11 times stronger than the slower plane?

Observe how much less you deflect your steering wheel at freeway speeds compared to half or less that speed on a slow road...

You use the term "turning moment", I guess in this context that's probably the same as "pitching moment"?  Just to be clear, that's not what actually determines turn rate; net pitching moment must be zero in a steady-state turn.

Why do you assume the same control surface deflection is used at all speeds?

lift force from the tail and lift increases quadratically with airspeed

Correct

That means that the faster jet will have a turning moment 11 times stronger than the slower plane?

No, because the aerodynamic force depends also on how many degrees the control surface is deployed, more or less in a linear manner. That means that instead of deploying the control surface of say 11° as you do at low speed, you deploy it only 1° i.e. 11 times less in order to compensate for the 11 times higher speed's contribution.
Changes in altitude ($\rho$), comprimibility effects (Mach > 0.3) and structural deformations modify this simple linear relationship but the main idea still holds i.e. at higher speed you need lower deflections.


text:
Is Flight Idle a constant?
Is "Flight Idle" for a jet engine a constant N1% value or does it vary with Altitude, and OAT?

This will vary from engine to engine and with modern engines controlled by computers for max fuel efficiency, the computer will constantly adjust the idle during the descent unless you manually select otherwise. However a minimum idle speed is necessary to prevent flame-out, and is as high as 70%** during severe icing conditions although 55% is the minimum. There are also different idle regimes, flight idle, approach idle and ground idle, controlled automatically.
The last aircraft that I flew, the B727, did not have any fancy FADEC and we manually closed the throttles at top of descent. The fuel control unit would adjust the fuel flow throughout the descent to keep a minimum 55% N1. This was evident from observing the fuel flow increase throughout the descent even though the throttles were at idle. If we needed more N1 due to icing, we would have to advance the throttles manually. Some planes had autothrottle but I don't think it compensated for icing.
Approach idle is also controlled automatically and is somewhat higher to allow a quick spool-up in the event of a go-around. It is deactivated after touchdown.
The 737Ng has similar regimes controlled by the EEC (Electronic Engine Control).
** Thrust requirements for for engine and wing anti-ice:

If Icing conditions exist with TAT -7° or above: 55% N1
If Icing conditions exist with TAT below -7° or moderate to severe icing observed at any temperature: 70% N1
Only one outboard engine supplying bleed air for wing 75% N1 on that engine.

To answer your question below, a jet engine works much the same as a piston engine wrt air/fuel ratio and the compression ratio is determined by its construction (see NASA). In a jet engine however you don't have a butterfly valve to vary air input, you can only vary fuel input-(there are exceptions with bleed-off valves, but let's keep it simple). The speed at which the engine turns determines air input and this speed is regulated by the amount of fuel injected into the combustion chamber. The jet engine will automatically settle at an equilibrium speed when the best air/fuel ratio is achieved.
So assuming an engine with only a variable fuel input (no automatic compensation for any variable parameters such as altitude)--- if for instance the altitude at start of descent is higher, less air is going to be taken in by the compressor, the fuel/air ratio will change resulting in a different engine speed than if the start of descent altitude was lower.
Ram air effect (Indicated airspeed) will also change the fuel/air ratio once again causing a different equilibrium engine speed.
Temperature will also affect the density of the air and cause a different rotation speed.
This is clearly unacceptable therefore some kind of governor must be provided to maintain stable parameters.
You can use the NASA engine simulator here to play around and test various scenarios.

"The fuel control unit would adjust the fuel flow throughout the descent to keep a minimum 55% N1." I thought Flight Idle was based on N2, not N1. Obviously I was wrong. How does it vary with Altitude and temperature?

It's N1, and my book says in severe icing to increase the N1 to 80% for 15 secs every 10 mins with engine anti-ice on. I will try find it in the manual.

@StamatisVellis You're correct - N2 keeps the engine running; N1 is the byproduct of that. For the CFM-56, flight idle in the descent is typically below 55% N1, by quite a bit. Maybe 55% N2. I'll see if I can grab some N1+N2 values in the descent later today & post them.

Just curious if that is -7°C or -7°F? Probably doesn't matter significantly, but...

@FreeMan That should be Celsius. Everything on the linked page uses "Degrees C", nothing in Fahrenheit.

A turbofan is really just a free-turbine turboprop like A PW120 but with a fixed pitch, ungeared, shrouded propeller with oodles of blades.  N1 equates to "propeller RPM" and N2 equates to "gas generator RPM".

@RalphJ I took the following notes for the 737 in class but I didn't note whether they were N1 or N2 ... Ground idle approx 60%, Approach Idle approx 75 - 79% Flight Idle approx 72%

@Raffles  Those are N2 values. Way too high to be N1's. You fly an approach at ~ 58% N1, and that's well above idle.


text:
How is the B737NG Autopilot controlling pitch?
In particular, does the Autopilot in a B737NG control the pitch only via trim adjustment, or first via the elevators and then trim?

In most airplanes, the AP flies the same way the pilot would.  It makes elevator inputs to achieve a condition, and if it has to hold the input to keep that condition, it works the trim so that it can relax the input.  So, elevator, followed up with trim where required to zero the elevator servo load.

This is from the B737NG airplane manual. Boeing doesn't offer the technical drawings in the pilot manuals, one would have to have access to the maintenance manuals. Boeing is very sticky about their material being published on the internet.

Autopilot Flight Director System (AFDS)
The AFDS is a dual system
consisting of two individual flight control computers (FCCs) and a
single mode control panel. The two FCCs are identified as A and B. For
A/P operation, they send control commands to their respective pitch
and roll hydraulic servos, which operate the flight controls through
two separate hydraulic systems.

This is a brief explanation of an autopilot system such as on the B737 from this website.

Aircraft with hydraulically actuated flight control systems have
autopilot servos that are electro-hydraulic. They are control valves
that direct fluid pressure as needed to move the control surfaces via
the control surface actuators. They are powered by signals from the
autopilot computer. When the autopilot is not engaged, the servos
allow hydraulic fluid to flow unrestricted in the flight control
system for normal operation. The servo valves can incorporate feedback
transducers to update the autopilot of progress during error
correction.

So it is not clear if the B737 AP works only through the horizontal stabilizer (trim) or elevators AND horizontal stabilizer. "Flight controls" could be meaning both. I guess someone who flies it would know though, simply by watching if the yoke moves back and forth during AP operation :-)

It is quite clear. The 737 NG autopilot controls the elevator and pitch trim, just like a pilot would.

@StamatisVellis The hydraulic servo described in this answer is acting on the elevator (for pitch) and ailerons (for roll). Additionally, the autopilot has control over the electric motor driving the jackscrew of the THS. And yes, the yoke does move as a result of autopilot inputs (based on FCC signal to the elevator feel and centering unit).


text:
In a B737 NG, when a TO is flown with an Assumed Temperature N1, is the subsequent CLB N1 also adjusted (lowered) accordingly?
The Title is my question. Because I think that if one uses a very high Assumed Temperature, the subsequent Max CLB N1 maybe higher that the TO N1.

Possibly, but not necessarily.
The climb thrust can be selected on the FMC N1 Limit page. The choice is between CLB, CLB-1 and CLB-2. The climb thrust is then reduced according to the selection:

7 - Climb (CLB)
Push – selects full rated climb thrust limit. [...]
8 - Reduced Climb (CLB–1 and CLB–2)
Push – selects the associated reduced thrust climb mode.
CLB–1 provides a climb limit reduced by 3% N1 (approximately 10% thrust).
CLB–2 provides a climb limit reduced by 6% N1 (approximately 20% thrust).
Deletion results in the selection of CLB thrust.
Manual selection of a climb thrust rating overrides the automatic selection.

(Boeing 737 NG FCOMv2 11.40.47 - Flight Management, Navigation - FMC Preflight)
When a takeoff thrust derating or an assumed temperature is entered, the FMC automatically selects a corresponding climb derating. And yes, the climb derating is computed such that it is below or equal to the takeoff thrust:

Derated Thrust Climb
Two fixed climb thrust derates can be selected on the N1 LIMIT page. CLB–1
provides a climb limit reduced by 3% N1 (approximately 10% thrust). CLB–2
provides a climb limit reduced by 6% N1 (approximately 20% thrust). The
reduced climb setting gradually increases to full rated climb thrust by 15,000 feet.
In cruise, the thrust reference automatically changes to CRZ. The reference can be
manually selected on the N1 LIMIT page.
Use of an assumed temperature reduced thrust takeoff or takeoff derate affects the
FMCs climb derate computation. If a reduced thrust takeoff has been specified on
the TAKEOFF REF page, the FMC will re-compute CLB-1 and CLB-2 values as
required to avoid a climb N1 value greater than the reduced thrust takeoff N1
value.

(Boeing 737 NG FCOMv2 11.32.4 - Flight Management, Navigation - Flight Management Computer; emphasis mine)
However, if the pilots manually select CLB after the automatic selection of a derated climb thrust, then the climb thrust can actually increase over the TO thrust.

And higher than FL150 it by default reverts to CLB, regardless of being in CLB1 or CLB2?

@StamatisVellis - That's correct. The CLB-1 and 2 schedules match up with CLB at 15,000' and above.

GE calls this process of eliminating the derate 'fast taper' when it happens around 14,000 ft and 'slow taper' when it merges around 27,000 ft. This is one of many options that the Operator chooses and freezes. Infact the %derate is another Operator choice.


text:
What would be the expected approximate ROD when descending at 250 kt IAS using LVL CHG at 10,000 ft, assuming a GW of 60t?
The question refers to a B737NG but I suppose most similarly sized airliners would show a similar ROD under the circumstances.

A descent at idle power and 250 knots yields about 1,500 feet per minute in the 737. Perhaps a bit less in the Max (maybe 1,300 - 1,400 fpm) with its lower drag profile, and a bit more (like 1,600 fpm) in a Classic.
Source: personal experience flying 737's.


text:
Does the Autopilot switch to ALT ACQ mode at a fixed altitude difference from target altitude?
For example, if climbing (or descending for that matter) at 3500 fpm, will the AP switch to ALT ACQ mode at the same point it will as when climbing or descending with 1000 fpm? Or does the point of the switch is variable and depends on the ROC or ROD?
I am specifically interested in the B737NG.

The simple answer is that autopilots are designed to fly the aircraft in the same way that a human pilot would.....only more accurately!
If you were climbing/ descending at 3500fpm you’d anticipate the level off earlier than if climbing/descending at 1000fpm or you’d risk exceeding g limits and it wouldn’t be a very smooth transition.
Autopilots, including the 737NG, take into account the ROC/ROD to ensure a smooth transition to level flight so yes ALT ACQ engagement will vary.


text:
What happens if the crew do not set a FLT ALT in the cabin pressurization panel and leave it at zero but AUTO is still selected?
On the 737NG, will the cabin maintain a lower altitude than the plane or will cabin altitude equal aircraft altitude?
Will there be ANY cabin pressurization or none at all?
When will the HORN sound?
I know this is extremely unlikely to happen but am posing the hypothetical question in order to better understand how the system works.


text:
Does the optimum LRC speed increase or decrease as the GW of the aircraft decreases during a long range flight?
I do not know what defines the optimum LRC speed for each aircraft, aeronautically speaking.
I suspect it has something to do with optimum AoA but even then I am not sure if the LRC speed should increase or decrease as the GW is being reduced during the flight.